An attractive, stable head of foam is considered an important quality factor for beer by many consumers. Therefore, brewers routinely analyze the foam characteristics of their beer as part of the quality control of the product.
The principal aim of foam analysis is to measure what customers will notice when they pour the beer. The visually perceptible properties of foam quality include the height of the foam or head formation, the stability of the foam, the foam texture or bubble size, the lacing of the foam and foam adhesion.
It has been found that the size of the foam head is largely dependent on the gas content of the beer. However, the length of head retention, or life, and the clinging of the foam to the walls of the container can be affected by minor foam and surface active constituents and the presence or absence of foaming factors which are derived from brewing ingredients and processing steps.
Various methods and apparatus are commercially available for measuring the foam characteristics of beer. However, the most popular techniques use special foam making equipment and do not recommend forming the foam as the customer would, by simply pouring the beer from a bottle or can into a clear measurement container. Commonly used methods bubble carbon dioxide through the liquid beer or sonicate the liquid using ultra sound to excite the beer and produce foam. Another technique ejects liquid beer through a special nozzle.
Once the foam was created different approaches have been used to measure the height of the liquid and/or foam. The simplest generates the foam in a graduated vessel and a technician takes measurements by eye. Automatic systems have been devised which use conductivity or optical sensors to detect the foam height. For example, one system moves a line scan camera up and down a clear container to detect the levels of the liquid and foam therein. However, the methods may not accurately sense the amount of the foam by merely detecting its height. When the foam boundary is uneven, it is difficult to get a good measurement of the foam layer by simply sensing the height at one point.
Evidence that nine of the commercially available methods or apparatus is completely satisfactory can be found in the continued efforts to measure foam stability, in some cases using exotic new equipment. For example, in an article in the American Society Brewing Chemists Journal, Volume 48, No. 4, 1990, Pages 139-122, a method of evaluating beer foam characteristics using magnetic resonance imaging (MRI) is described. The method depends upon the paramagnetic properties of neutrons and protons of some of the atomic nuclei present. In the technique, the beer sample is poured gently down the side of a tube and then sonicated to form a foam which is analyzed using MRI.
The described prior art methods make the foam very differently than the way beer is consumed and measure the foam characteristics indirectly. There is a need for a method and apparatus which makes the foam in the same manner as a consumer and which directly evaluates the visually perceptible properties of a foam.